This invention relates to a solvent composition. In a more particular aspect, this invention concerns itself with a solvent mixture particularly adapted for use in dissolving and removing cured polyurethane resinous coatings such as paints and foams from metal or plastic substrates.
Polyurethane resins find wide use in a variety of industrial applications. They are a class of polymeric, synthetic resins that can be cured in accordance with well known and conventional curing techniques to produce a variety of products such as rigid, semi-rigid or flexible foams; hard, glossy coatings relatively resistant to solvents; rubbery and fibrous materials; as well as thin, paint-like compositions. Perhaps their most important use in modern technology resides in their application as cured foams in rug backing, upholstery material for furniture, commercial and residential insulation and as insulating materials for aircraft components. The cured polyurethanes also are of importance as conformal coatings and foam encapsulants for electronic circuit boards and other electronic components.
Unfortunately, the solvent resistance of cured polyurethanes presents certain problems. There is great difficulty in removing the hard, protective coatings or encapsulants from electronic components in order to effect repair or replacement of any of the individual units making up the electronic component. Heretofore, it was necessary to grind or severely abrade the cured coatings in order to effect their removal or, alternatively, rely on corrosive solvents which utilized strong acid or basic catalysts as part of the solvent mixture. Often times, the use of grinding techniques or strong solvents resulted in excessive damage to the electronic component and corrosion often occurred resulting in even greater damage. As a result, the repair or replacement of component parts could not be undertaken and the components had to be discarded at a great economic loss.
In order to avoid economic losses, hazardous health conditions from corrosive solvent vapors and health hazards from the pyrolsis of conformal coatings, it was found necessary to develop a solvent mixture that would be effective in dissolving and removing cured polyurethane resins whether in the form of a thick coating, paint-like coating, foam encapsulant or foamed structure. As a result of a research effort generated for the purpose of overcoming the problems previously encountered in removing polyurethane resins, it was found that a solvent mixture containing dichloromethane, dimethyl formamide and methanol could be used to overcome the problems associated with prior methods.